title: Cellular internalization and mechanism of cytotoxicity of ¹³¹I-rituximab in Raji cells.
abstract: Rituximab labeled with radioiodine (¹³¹I-rituximab) has a large potential to be employed for targeted therapy of non-Hodgkin's lymphoma. Studies of parameters such as cellular internalization, stability of ¹³¹I-rituximab bound to CD20 receptor of tumor cells, and the mechanism underlying cytotoxicity induced by ¹³¹I-rituximab will be useful for better clinical application. In this article we describe the efficacy of ¹³¹I-rituximab in CD20-expressing Raji cells. Rituximab labeled with ¹³¹I was purified on a PD-10 column and characterized using high-performance liquid chromatography and paper electrophoresis. Raji cells treated with ¹³¹I-rituximab (1.85 MBq for 2 hours) were washed then incubated. The culture medium collected from treated cells showed increased radioactivity over a longer period (>6 hours), probably due to the deiodination/degradation of ¹³¹I-rituximab. The tumor cells treated with ¹³¹I-rituximab showed time-dependent internalization of radioactivity, and at 12 hours the radioactivity was almost equally distributed in the membrane and cytoplasm. At 24 hours ~70% of the radioactivity was internalized. Cellular toxicity after ¹³¹I-rituximab treatment showed a time-dependent increase in toxicity as estimated by lactate dehydrogenase. Tumor cells treated with ¹³¹I-rituximab showed significantly higher toxicity and apoptosis compared with the those treated with the same concentration of unlabeled rituximab. The increased apoptotic death in cells treated with ¹³¹I-rituximab was associated with cleavage of poly ADP ribose polymerase and upregulation of p53 protein. This study provides a deeper understanding about the cellular internalization/stability of ¹³¹I-rituximab bound to the CD20 receptor and its efficacy in killing Raji cells.
authors.affiliation: Radiopharmaceuticals Division, Bhabha Atomic Research Centre, Mumbai, India.
authors.forename: Chandan
authors.initials: C
authors.lastname: Kumar
authors.forename: Badri N
authors.initials: BN
authors.lastname: Pandey
authors.forename: Grace
authors.initials: G
authors.lastname: Samuel
authors.forename: Meera
authors.initials: M
authors.lastname: Venkatesh
mesh_terms: D058846:Antibodies, Monoclonal, Murine-Derived / Q000493:pharmacokinetics / Q000494:pharmacology*; D018951:Antigens, CD20 / Q000378:metabolism; D000970:Antineoplastic Agents / Q000493:pharmacokinetics / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D004249:DNA Damage / Q000187:drug effects; D006801:Humans; D016393:Lymphoma, B-Cell / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D000069283:Rituximab; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20; D000970:Antineoplastic Agents; D016159:Tumor Suppressor Protein p53; D000069283:Rituximab; D011065:Poly(ADP-ribose) Polymerases; C507388:131I-rituximab